The present invention relates generally to fuel control systems and, more particularly, to a system for rationalizing the alcohol content of the fuel of a flexible fueled vehicle.
Alternative fuel vehicles are becoming commonplace in response to environmental and energy conservation concerns. Alcohol in the form of ethanol or methanol is combined in various percentages with gasoline to produce one type of alternative fuel. The vehicles capable of operating on more than one blend of gasoline and alcohol are referred to as flexible fuel vehicles. These vehicles may have some capability to adjust various engine operating parameters to compensate for the effects of one alcohol fuel blend over another including the possible use of gasoline unblended with alcohol.
This includes adjustment to the air to fuel mixture in order to maximize engine performance and to fully burn the fuel in use. The ideal air to fuel ratio in an internal combustion engine is typically considered to be the ratio of mass flow rate of air to mass flow rate of fuel inducted by an internal combustion engine to achieve conversion of the fuel into completely oxidized products. The chemically correct ratio corresponding to complete oxidation of the products is called stoichiometric. If the air/fuel ratio is less than stoichiometric, an engine is said to be operating rich, i.e., too much fuel is being burned in proportion to the amount of air to achieve perfect combustion. Likewise, if the air/fuel ratio is greater than stoichiometric, an engine is said to be operating lean, i.e., too much air is being burned in proportion to the amount of fuel to achieve perfect combustion. Since alcohol fuels require a lower air/fuel ratio than pure gasoline at stoichiometric, the engine must be compensated for in the rich direction. The amount of compensation increases as the percentage of alcohol in the fuel increases. For example, an engine operating on E85 (a blend of 85% ethanol and 15% gasoline) requires approximately 1.4 times the amount of fuel relative to gasoline at stoichiometry due to a lower energy content of the ethanol.
Various prior art methods and systems are already disclosed for determining the amount or percentage of alcohol in the fuel of a flexible fuel vehicle. Some of these systems utilize a composition sensor to measure the composition of the fuel used. A problem with these composition sensor based systems is the advent of sensor failure or miscalculation. This could result in the engine control system receiving faulty data upon which the engine is operated.
Other systems xe2x80x9clearnxe2x80x9d the alcohol content of the fuel through an oxygen sensor in the exhaust system that measures the oxidation of combustion byproducts in the exhaust. A potential problem with these xe2x80x9clearnxe2x80x9d based systems is the effect of a malfunction of a component of the system that effects the combustion byproducts or even a malfunction of the oxygen sensor. For example, a clogged fuel filter or injector drift could effect the learned determination of the alcohol content by causing a faulty fuel system and resulting in lean combustion. A system could under these and other circumstances learn into the alcohol realm and effect the engine control system.
Therefore, there is a need for a system that will rationalize the alcohol content without reliance on a fuel composition sensor. Further, a system is needed that will rationalize the alcohol content as a backup to any sensor or learned result.
It is therefore an object of the invention, a rationality system, to rationalize (i.e. check for accuracy) the alcohol content of the fuel in a flexible fueled vehicle. It is a further object to provide a backup to a learned (i.e. oxygen sensor) or fuel composition sensor based system in determining the possible alcohol content of the fuel. A further object of the invention is to allow activation of warning systems and/or other action if the system detects fault in the determination of the alcohol concentration in the fuel.
In operation the invention is activated by a triggering event such as an addition of fuel to the fuel tank. The rationality system then calculates the possible concentrations of alcohol in the fuel based on the possible fuels added. Next, the rationality system compares the alcohol content as determined by a learned based system or a sensor based system to the possible concentrations of alcohol. If the determined alcohol content is too far from the possible concentrations of alcohol then a fail counter is incremented to show a failure to properly determine the fuel alcohol content. If the fail counter reaches a predetermined level then action is taken to warn the vehicle operator of the fault. Diagnostic systems may also be enabled or disabled depending on whether the alcohol content of the fuel is within the alcohol realm.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.